1. Field of the Invention
The invention relates in general to a circuit system for a fan tray module. In particular, the invention relates to a hot-swap circuit system for a fan tray module.
2. Brief Discussion of the Related Art
At the moment of hot plugging a fan tray module in an application system and activating the fan tray module, the application system will generate voltage spikes and inrush currents while sending out sparks due to the power supply terminal thereof suddenly taking the load of the fan tray module. The voltage spikes and inrush currents will mistakenly trigger the over-voltage protection device and the over-current protection device installed in the power supply terminal of the application system, and therefore crash the application system.
To avoid the described problems, a hot-swap circuit generally is provided to a fan tray module such that the fan tray module carries out a soft-start operation when plugged into an application system, thereby suppressing voltage spikes and inrush currents generated in the application system at the moment of activating the fan tray module.
In FIG. 1, a conventional hot-swap circuit 1 performs a soft-start operation of a fan tray module 16, using an analog controller IC (integrated circuit) 11 to drive an n-channel metal-oxide semiconductor field effect transistor (MOSFET) 12 serving as a transistor switch, wherein a Zener diode (D2) 13 works as an over-voltage protection device and a resistor set (R10, R12, R13) 14 works as an over-current protection device.
However, the conventional art shown in FIG. 1 has the follow drawbacks. First, the analog controller IC 11 requires costly design and is expensive. Second, the analog controller IC 11 cannot provide a wide range of voltage supply. It can only provide the most negative voltage of −3 volts, and therefore the fan tray module is vulnerable to transient negative voltage when being hot-plugged into the application system (not shown in FIG. 1). Thirdly, the driving capability of the analog controller IC 11 is inadequate for the transistor switch 12. Fourthly, suppression for the voltage spikes and inrush currents is limited when the hot-swap circuit 1 is applied to the fan tray module operating in large current and voltage conditions.
In addition, the hot-swap circuit 1 lacks a discharging loop or path and hence a part of the inrush currents accumulate in the hot-swap circuit 1. The accumulated inrush currents may trigger a current protection device of the application system and crash the application system when the fan tray module 16 is frequently inserted and removed from the application system. For example, lightning interference may trigger the protection mechanism to shut down the power source supplied to the application system. When the power source is quickly recovered and fed to the application system, abnormally large inrush currents will flow into the application system and crash the application system, because the accumulated charges stored in the capacitor set (C5˜C8) 15 of the hot-swap circuit 1 are not completely discharged.